1. Field of the Invention
The invention relates generally to inductive coupling, and more particularly to transformers where there is relative motion between the primary and secondary winding and minimal reaction forces therebetween.
2. Description of the Prior Art
The invention described herein has particular utility in applications where electrical power is coupled from a stationary location to a moving location with a minimum of interaction between the stationary and moveable components. The invention is principally applied to transfer power across magnetically suspended interfaces, where small disturbance forces might impact the magnetic control forces, and where motions over as many as six degrees of freedom are required over a limited range.
Known technologies for coupling electro-magnetic energy across a moving boundary or interface consist of solenoid and rotary transformer type structures. In U.S. Pat. No. 4,117,436, Torqueless Relatively Moving Transformer Windings, issued to A. G. MacLennan, a transformer comprised of primary and secondary windings axially disposed on a common axis and surrounded by a core of high permeability material is adapted to provide limited relative rotary motion between first and second transformer windings about the axis. The disadvantage of this device is the limited range of freedom of relative motion. Another structure is shown in U.S. Pat. No. 4,321,572, issued Mar. 23, 1982 to P. A. Studer. In the Studer structure, a rotary transformer has a fixed primary winding and a secondary winding rotatable through a gap in the core structure. The invention principally allows full rotational freedom without allowance for motion about other axes. However, the presence of the air gaps in the core of Studer's invention deteriorates electrical performance by greatly reducing the magnetizing inductance in relation to the leakage inductance, thereby requiring larger excitation currents and volume to perform a given power transfer, resulting in reduced efficiency.
The present invention improves over the prior art by providing a non-contacting structure that allows motion over six degrees of freedom, provides insignificant reaction forces with respect to the actual control forces applied to a stabilized structure attached thereto, requires no air gap in the core, and provides high efficiency over the required range of motion.